This invention relates to a trip device for an electric circuit breaker and, more particularly, to a trip device that relies upon a permanent magnet for holding a trip-controlling plunger in a withdrawn position and a tripping coil that, upon energization, develops flux that opposes flux from the permanent magnet, thereby effecting release of the plunger.
References of interest with respect to this invention are the following: U.S. Pat. Nos. 3,671,893--Edgar et al.; 3,675,167--Ellenberger; 3,693,122--Willard; and 3,783,423--Mater et al.
In a typical construction of such a trip device there is a flux diverter located between the permanent magnet and the plunger. The diverter is designed so that most of the flux developed by the tripping coil when energized is forced to follow a path through the diverter so as to protect the permanent magnet from demagnetization by such flux. If the diverter in the typical trip device is to have the desired effectiveness in protecting the permanent magnet, it must present a relatively low reluctance path to flux from the tripping coil. But if such a low reluctance path is present, it is difficult to efficiently utilize the flux developed by the permanent magnet for holding the tripping plunger since a large portion of such flux from the permanent magnet will be shunted through the diverter without contributing to the plunger holding action.